IRVINE – The California Supreme Court’s ruling allowing gay marriage is based on sound constitutional principles and allowing Prop. 8 to pass would be an “incalculable blow to progress,” the dean of UCI’s law school said Sunday.

Prof. Erwin Chemerinsky spoke to about 100 people Sunday as an invited guest of Irvine United Congregational Church. The church identifies itself as a “liberal and inclusive” congregation that includes gay and lesbian members.

His speech was the latest in a mounting debate over Prop. 8, the Nov. 4 California ballot measure that would amend the state constitution to define marriage as between a man and a woman and would eliminate the right of same-sex couples to marry.

Chemerinsky said Prop. 8 would not only define the issue of gay marriage in California, but would have a nationwide influence.

“If Prop. 8 is defeated, I believe that within my lifetime we will see a majority of states allow same-sex couples to marry,” said Chemerinsky, 55, a renowned constitutional scholar who became the founding dean of UCI’s Law School earlier this year, after stints at USC and Duke University.

“If it is approved, that progress will be halted,” he said, “The stakes are enormous.”

On that point, both sides agree.

Sonja Eddings Brown, a spokeswoman for the Yes on 8 campaign, called this the nation’s second most important election on Nov. 4 and one that indicates the country is at a “cultural crossroads.”

Orange County has proven to be among the top fundraising regions in the state in the effort to ban gay marriage. And in recent days, statewide polls have indicated that voters are likely to approve the measure.

“For many of us, it’s just a matter or what’s right. We were always taught and we want to teach our children that marriage is something sacred between a man and woman – only,” said Ted Mulvaney, an Irvine resident who lives near the church where Chemerinsky spoke but did not attend the speech.

The Rev. Paul Tellstrom, pastor at the church, said his parishioners have been working phone banks, distributing “No on 8” signs and even approved a church resolution opposing the proposition.

“For us, it’s a moral issue,” he said.

Chemerinsky said he worries that many people are basing their opinions on bad information.

Chemerinsky disagrees with several of the principles of the Yes on 8 campaign, including:

– That allowing same sex marriage is destructive to the institution of marriage.

“I don’t understand how my marriage is affected by others expressing love and commitment to each other … If anything, it’s more affirming,” he said.

– That it is harmful to children

Allowing marriage encourages family stability, he said.

– That clergy will be forced to conduct same-sex marriages.

“Pastors and rabbis, just like some won’t perform inter-faith marriages, can decide who they will marry or not,” he said.

Church members said they were invigorated by Chemerinsky’s speech and will step up their efforts to get out the “No on 8” vote.

“I feel the U.S. is about freedom,” said Carol Lechich-LeMar of Irvine. “And I don’t want to deny freedom to anybody.”

Mulvaney, 48, said he respects that some people will disagree, but he will continue to fight for a yes vote.

“Interesting that the pastor says he thinks it’s a moral issue,” he said. “My morals tell me that marriage should stay between a man and woman. That’s why I think you see the shift in polls lately. More people are standing up for what they believe.”